One or more embodiments of the present invention pertain to methods for use in fabricating integrated circuit device structures on a substrate, and, in particular, to methods for etching an organic anti-reflective coating.
Critical dimensions and geometries of semiconductor devices have decreased steadily in size since they were first introduced. Although, currently, most semiconductor devices are fabricated with feature sizes of about 0.18 xcexcm-0.25 xcexcm, it is desirable to produce semiconductor devices, for example, semiconductor integrated circuit chips, with smaller feature sizes, such as 0.13 xcexcm microns and lower. Fabricating such semiconductor devices includes forming a patterned thin film or layer on a base substrate of the device by chemical reaction of gases. When patterning thin films, it is desirable that fluctuations in line width and other critical dimensions be minimized. Errors in these critical dimensions can result in variations in device characteristics or open-/short-circuited devices, thereby adversely affecting device yield. Some manufacturers now require that variations in dimensional accuracy of patterning operations be held to within 5% of dimensions specified by a designer.
A typical fabrication process utilizes photolithographic techniques to pattern films or layers. These techniques typically entail fabricating a pattern in a photoresist layer deposited on a substrate. With the photoresist pattern acting as a mask, underlying layer(s) are further processed. For example, the underlying layer(s) may be doped or etched, or other processing may be performed.
As is known, some photolithographic techniques entail the use of monochromatic radiation to produce the patterns. However, as a substrate is processed, a topology of the substrate""s upper surface becomes progressively uneven. This can cause reflection and refraction of the monochromatic radiation, resulting in exposure of some of the photoresist layer beneath portions of the mask. As a result, the uneven surface can alter the pattern transferred to the photoresist layer, thereby altering desired dimensions of structures fabricated subsequently.
As is also known, when a photoresist layer is deposited on a reflective underlying layer, and is exposed to monochromatic radiation, standing waves may be produced within the photoresist layer. The existence of standing waves in the photoresist layer during exposure can cause roughness in vertical walls formed when sections of the photoresist layer are removed during patterning. This can translate into variations in line widths, spacing, and other critical dimensions.
The use of an anti-reflective coating (xe2x80x9cARCxe2x80x9d) is one technique currently used to help reduce and/or eliminate the standing waves. An ARC""s optical characteristics are such that reflections occurring at inter-layer interfaces are minimized. One type of ARC is a titanium nitride anti-reflective coating (xe2x80x9cTiN ARCxe2x80x9d). A TiN ARC is typically used with substrates that have conductive features (for example, conductive features that include an aluminum alloy) used to electrically connect devices formed on the substrates. The conductive features are typically formed over a barrier-adhesion layer, and under a TiN ARC.
It has been determined that (for certain applications) a TiN ARC (by itself) does not satisfy processing requirements, and as a result, another anti-reflective layer, such as an organic anti-reflective coating (xe2x80x9cOARCxe2x80x9d), is typically spun on top of the TiN ARC. The substrate with the OARC is then processed using an etch process to selectively etch portions of the substrate. The etch process entails introducing a selected process gas into a processing chamber, and producing a plasma of the process gas. The plasma selectively etches the substrate, and creates volatile etch by-products that are exhausted from the processing chamber. In accordance with an etch process used for device dimensions of 0.25 xcexcm and smaller, a process gas used to etch the OARC (xe2x80x9cOARC-openxe2x80x9d etch) is a mixture of gases such as, for example, Cl2/(CHF3 or CF4), and a process gas used to etch an aluminum alloy layer (xe2x80x9cAl main etchxe2x80x9d) is a mixture of gases such as, for example, Cl2/BCl3/CHF3. The above-described OARC-open etch and Al main etch create a problem because of the following. During the Al main etch, AlCl3 containing etch by-products are deposited in the processing chamber (for example, on a dome of a Decoupled Plasma Source (xe2x80x9cDPSxe2x80x9d) Metal Etch chamber available from Applied Materials, Inc. of Santa Clara, Calif.). Further, the OARC-open etch creates a xe2x80x9cfluorine-richxe2x80x9d environment in the processing chamber. The problem arises because the fluorine reacts with the AlCl3 containing etch by-products to form AlF3, containing by-products, and AlF3 containing by-products are difficult to remove from the processing chamber (for example, by use of in-situ chamber cleaning processes available with the DPS Metal Etch chamber). As a result, the AlF3 containing by-products are a potential particle source, and thus the mean wafer between clean (MWBC) is reduced.
An additional problem with the use of the above-described OARC-open etch process and Al main etch process is that: (a) during the OARC-open etch, CHF3 interacts with the photoresist mask and substrate material to form polymers which are deposited, for example, on the photoresist; and (b) during the Al main etch process, CHF3 interacts with Al and forms AlF3 that coats the polymers and the aluminum features. Later, when the substrate undergoes processing to strip the photoresist mask, AlF3 coated polymers may remain as an unwanted structure that is sometimes referred to as xe2x80x9crabbit ears.xe2x80x9d Thus, the strippability is affected.
Although O2 might appear to be useful in solving the above-described problems its use creates new problems. Namely, O2 reacts with BCl3 that is utilized in the Al main etch. This creates a problem because this reaction may clog up gas lines or a gas manifold used to dispense processing gases into the processing chamber.
One or more embodiments of the present invention advantageously solve one or more of the above-identified problems. In particular, one embodiment of the present invention is a process for etching an organic anti-reflective coating on a base of a substrate, the process comprising steps of: (a) placing the substrate into a processing chamber; (b) introducing into the processing chamber a processing gas comprising one or more of carbon monoxide (CO), carbon dioxide (CO2), and sulfur oxide (SO2); and (c) forming a plasma from the processing gas to etch the organic antireflective coating layer.